1. Field of the Invention
The present invention relates generally to a method for depositing hard carbon film onto a substrate, and especially to such a method in which the hard carbon film is a thin film of diamond crystal and the substrate if os non-diamond material that is kept at low temperature.
2. Description of the Prior Art
In recent years, hard carbon films of diamond or diamond-like films have been studied. Such diamond film and diamond-like films are formed by using the so-called CVD method (hot filament CVD, microwave plasma-assisted CVD, etc.) or the ion-beam method (ion beam deposition, ion beam sputtering, etc.).
In order to make the diamond film by the conventional methods, substrate must be raised to a high temperature of several hundred degrees (.degree.C.). For the application to the semiconductor industry, the diamond thin film should be formed under a low temperature condition (&lt;400.degree. C.). Furthermore, the diamond films formed by conventional methods are polycrystalline and each crystal has randomly-oriented crystal axes. For application to the diamond semiconductor devices, it has been desired that a single crystal diamond film be formed on the substrate which is not diamond.
The conventional processes of making diamond crystal film have problems of necessitating a high temperature and difficulty in controlling the crystal axes of diamond deposited onto the substrate. Heretofore, no one has succeeded in making diamond crystal at room temperature.
There were reports that diamond-like amorphous hard carbon films were obtainable on substrates which were kept at low temperature. FIG. 1 schematically shows, one of the conventional methods for making the diamond-like film, using dual ion beam sputtering apparatus. In using this conventional apparatus, an Ar ion beam 2 is issued from a sputtering ion source 1 and bombards a carbon target 3, from which carbon particles 4 are sputtered and impinge on a substrate 5. On the other hand, another ion beam source 6 issues another Ar ion beam 7 which bombards the surface of the substrate 5. By means of such a dual ion beam sputtering process, a hard carbon film 51 is formed on the surface of the substrate 5. The bombarding ion beam 7 makes carbon particles, which are sputtered from the target 3 and deposit on the substrate 5, into a diamond-like amorphous hard carbon film 51. The mechanism, by which the bombarding substrate with the ion beam 7 produces the desired effect, is not yet revealed so far, but it is known that a use of a bombarding ion beam besides an impinging of carbon particles produces hard carbon film.
The conventional processes of making the diamond-like amorphous film have problems of necessitating a two ion source or special ion source which issued a carbon ion beam, and difficulty in controlling the physical properties of the obtained diamond-like film. The incident angle of the bombarding ion beam on the surface of the substrate have never been considered. These diamond-like films do not contain diamond crystals. Diamond crystals have never been made at room temperature.